1. Field of the Invention
The present invention relates to a punching unit for boring a pattern, a reference hole or the like in a printed substrate, a flexibility film, a ceramic green sheet or the like, and more particularly to a punching unit suitable for boring a hole in a workpiece which easily spreads like the ceramic green sheet when a pressing force is applied.
2. Description of the Related Art
Heretofore, a punching unit of this type has been constructed such that there are, at the tip end-side upper part of the machine frame, provided a punch holding die together with a striking driving source, and at the tip end-side lower part, provided a die holding die corresponding to the punch holding die respectively and that a workpiece is carried in between the punch holding die and the die holding die to bore a hole into a required pattern, a reference hole or the like.
This punching unit is, on the machine base, provided in a necessary quantity close to one another side by side, and its punch holding die is equipped with a stripper mechanism which continuously presses (sandwiches) the workpiece between the die holding die and the punch holding die during a period of time from immediately before the punch comes into contact with the workpiece to a time at which the punch is drawn out.
For a striking driving source for the punch, an air cylinder, or an electric motor (for example, servo motor) is used.
In the air cylinder, pressure of air to be compressed is utilized as a driving force, and since air is a compression medium although low in cost, it is difficult to say that a movement of a piston for transmitting a striking force to a punch always coincides with the air pressure. As striking is continuously performed, there arises minute deviation in interlocking relation between supply and exhaust of air pressure for moving the piston up and down, thus making it impossible to expect punching at equal speed at all times. Actually, a problem for deteriorating the quality of the hole such as a punch bounding with minute amplitude at a punching bottom dead center is caused.
On the other hand, if an electric motor is used, the above described problem of air cylinder will be able to be solved.
In either case, however, since pressing (sandwiching) of the workpiece is continued during a period of time from immediately before punching to a time at which the punch is drawn out, a time for pressing by a stripper plate causes time loss which deteriorates the punching efficiency, deteriorating the productivity. In the case of, for example, ceramic green sheet which easily spreads, the pressing force spreads the workpiece, thus making it impossible to punch with high precision.
Also, an air passage which is connected to a punching hole of a die is connected to an air supply unit (for example, air compressor) provided in a factory where a machine base on which a punching unit is mounted is installed. An air path from the vicinity of the air supply unit to an air ejecting unit becomes long, and therefore, the response to air ejection is slow, and the pressure loss during air flow also becomes greater. For this reason, there has been also a problem that even if air is ejected toward the tip end of the punch at the bottom dead center at predetermined timing, air is not supplied at timing capable of peeling leavings and at predetermined air pressure and in a predetermined amount of air, but as a result, the punching operation is repeated while punching chips (shavings) adhere to the punch without being able to strip the leavings for reducing yields.
The present invention has been achieved in view of the above described conventional state of affairs, and is aimed to provide a punching unit capable of increasing productivity and yet not deteriorating the punching precision even for a workpiece which easily spreads.
Also, it is another object to provide a punching unit for preventing leavings rising.
Technical means instituted in order to achieve the above described object is characterized in that a punch ram is provided on the machine frame so as to be able to adjust the vertical moving height through the use of height adjusting means; the punch ram is provided with an electric motor which serves as a driving source; at the lower end of the punch ram, a stripper plate is mounted as a punch fixed die; a movable die holding a punch is disposed above the stripper plate so as to couple to the electric motor; and the electric motor is driven in a state in which the stripper plate is positioned close to the workpiece by the height adjusting means for boring a hole (First aspect).
In this case, the electric motor includes a servo motor, a linear motor, a stepping motor and the like.
According to the above described means, it becomes possible to cause the stripper plate at the lower end of the punch ram to approach in response to the workpiece to be punched by means of the height adjusting function of the punch ram using the height adjusting means. The stripper plate is caused to approach several xcexcm spaced from the workpiece in such a manner that the workpiece is not pressed, but yet the punch can be drawn out of the workpiece when the punch is rising. Therefore, the stripper plate which has been positioned close to the workpiece in accordance with the thickness of the workpiece to be punched does not press the workpiece, but reliably draws the punch during rising out of the workpiece to increase the punching efficiency by eliminating time loss caused by continued pressing by the conventional stripper plate. Thus, the striking driving force of the electric motor is transmitted to the movable die holding the punch.
Also, within the machine frame, there is preferably introduced an air passage for supplying air into the air ejecting unit provided in the die and within the machine frame, there is provided means for opening or closing the air passage through an electric signal from the electric motor (Second aspect).
In this case, means for opening and closing through an electric signal, for example, an electric switching valve is preferably constructed such that the interior of the machine frame is formed hollow and that within the machine frame, the electric switching valve is provided at a position close to the die holding die.
With such structure, the air path between the air ejecting unit and the means for opening and closing the air passage becomes very short.
Accordingly, the pressure loss at the time of air ejection is reduced to a minimum at the same timing as punching bottom dead center, and jet air from the air ejecting unit is accurately applied to the tip end of the punch to peel the punching chips (leavings).